Nonvolatile semiconductor memory transistor and method for manufacturing nonvolatile semiconductor memory

ABSTRACT

A nonvolatile semiconductor memory transistor includes an island-shaped semiconductor having a source region, a channel region, and a drain region formed in this order from the silicon substrate side, a floating gate arranged so as to surround the outer periphery of the channel region with a tunnel insulating film interposed between the floating gate and the channel region, a control gate arranged so as to surround the outer periphery of the floating gate with an inter-polysilicon insulating film interposed between the control gate and the floating gate, and a control gate line electrically connected to the control gate and extending in a predetermined direction. The inter-polysilicon insulating film is interposed between the floating gate and the lower and inner side surfaces of the control gate and between the floating gate and the lower surface of the control gate line.

RELATED APPLICATIONS

This application is continuation application of U.S. Ser. No.13/898,982, filed May 21, 2013, now U.S. Pat. No. 8,159,813, which is adivisional patent application of U.S. Ser. No. 13/163,319, filed Jun.17, 2011, now U.S. Pat. No. 8,471,327, which claims the benefit of thefiling date of Provisional U.S. Patent Application Ser. No. 61/367,903filed on Jul. 27, 2010. This application also claims priority under 35U.S.C. §119(a) to JP2010-168148 filed on Jul. 27, 2010. The entirecontents of these applications are hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a nonvolatile semiconductor memorytransistor and a method for manufacturing a nonvolatile semiconductormemory.

2. Description of the Related Art

A flash memory including a control gate and a charge storage layer anddesigned to inject electric charge into the charge storage layer usinghot electron injection, using Fowler-Nordheim current, or the like isknown. Memory cells of the flash memory record unit data “1” or “0”using the difference in threshold voltage, which depends on the chargestorage state of the charge storage layer.

In order to efficiently perform injection of electrons into the chargestorage layer and emission of electrons from the charge storage layer,that is, writing and erasing of unit data, the capacitive couplingrelationship between a floating gate and a control gate is important.The greater the capacitance between the floating gate and the controlgate is, the more effectively the potential of the control gate can betransmitted to the floating gate. Therefore, writing and erasing arefacilitated.

In order to increase the capacitance between the floating gate and thecontrol gate, a Tri-Control Gate Surrounding Gate Transistor (TCG-SGT)Flash Memory Cell illustrated in FIG. 46 has been proposed (for example,see Takuya Ohba, Hiroki Nakamura, Hiroshi Sakuraba, Fujio Masuoka, “Anovel tri-control gate surrounding gate transistor (TCG-SGT) nonvolatilememory cell for flash memory”, Solid-State Electronics, Vol. 50, No. 6,pp. 924-928, June 2006). Since the control gate of the TCG-SGT flashmemory cell has a structure that covers, in addition to the side surfaceof the floating gate, the upper and lower surfaces of the floating gate,the capacitance between the floating gate and the control gate can beincreased, and writing and erasing are facilitated.

However, in order to increase the capacitance between the floating gateand the control gate in the TCG-SGT flash memory cell illustrated inFIG. 46, it is necessary to increase the thickness of the floating gate.If the film thickness of the floating gate is small, it is difficult toincrease the capacitance between the floating gate and the control gate.

SUMMARY

Accordingly, the present invention provides a nonvolatile semiconductormemory transistor having a structure utilizing an island-shapedsemiconductor, in which the capacitance between a floating gate and acontrol gate can be increased, and a method for manufacturing anonvolatile semiconductor memory.

A first aspect of the present invention provides a nonvolatilesemiconductor memory transistor including an island-shapedsemiconductor, a floating gate, a control gate, and a control gate line.The island-shaped semiconductor has a source region, a channel region,and a drain region formed in the order of the source region, the channelregion, and the drain region from the side of a substrate. The floatinggate is arranged so as to surround an outer periphery of the channelregion in such a manner that a tunnel insulating film is interposedbetween the floating gate and the channel region. The control gate isarranged so as to surround an outer periphery of the floating gate insuch a manner that an inter-polysilicon insulating film is interposedbetween the control gate and the floating gate. The control gate line iselectrically connected to the control gate and extending in apredetermined direction. The inter-polysilicon insulating film isarranged so as to be interposed between the floating gate and a lowersurface and an inner side surface of the control gate and between thefloating gate and a lower surface of the control gate line.

Preferably, the nonvolatile semiconductor memory transistor furtherincludes a first insulating film arranged on the substrate so as to belocated below the floating gate, the first insulating film being thickerthan at least one of the tunnel insulating film and theinter-polysilicon insulating film.

A second aspect of the present invention provides a method formanufacturing a nonvolatile semiconductor memory including a floatinggate arranged so as to surround an outer periphery of an island-shapedsemiconductor with a tunnel insulating film interposed between thefloating gate and the island-shaped semiconductor, a control gatearranged so as to surround an outer periphery of the floating gate withan inter-polysilicon insulating film interposed between the control gateand the floating gate, and a control gate line electrically connected tothe control gate and extending in a predetermined direction. The methodincludes a step of forming a plurality of island-shaped semiconductorson a source line formed at a predetermined position on a substrate; astep of forming an insulating film between the island-shapedsemiconductors that are adjacent to each other and on the source line; astep of forming a floating gate film by depositing a conductive materialon the insulating film; a step of forming a resist on the floating gatefilm, the resist having a groove extending in a direction perpendicularto the predetermined direction in which the control gate line extends; astep of forming a floating gate for each of the island-shapedsemiconductors using the resist by separating the floating gate filmfrom a portion that is a lower region of the groove and that is on theinsulating film by etching; a step of forming a control gate for each ofthe island-shaped semiconductors, above two floating gates of adjacentisland-shaped semiconductors among the island-shaped semiconductors, soas to surround the outer periphery of the island-shaped semiconductor;and a step of forming the control gate line to connect the control gatesof adjacent island-shaped semiconductors among the island-shapedsemiconductors.

According to the present invention, it is possible to provide anonvolatile semiconductor memory transistor having a structure utilizingan island-shaped semiconductor, in which the capacitance between afloating gate and a control gate can be increased, and a method formanufacturing a nonvolatile semiconductor memory.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view illustrating a main part of anonvolatile semiconductor memory transistor according to an embodimentof the present invention.

FIG. 2A is a plan view of a nonvolatile semiconductor memory accordingto an embodiment of the present invention, FIG. 2B is a cross-sectionalview taken along line X-X′ of FIG. 2A, and FIG. 2C is a cross-sectionalview taken along line Y-Y′ of FIG. 2A.

FIG. 3A is a plan view illustrating a method for manufacturing anonvolatile semiconductor memory according to an embodiment of thepresent invention, FIG. 3B is a cross-sectional view taken along lineX-X′ of FIG. 3A, and FIG. 3C is a cross-sectional view taken along lineY-Y′ of FIG. 3A.

FIG. 4A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 4B is a cross-sectional view taken along lineX-X′ of FIG. 4A, and FIG. 4C is a cross-sectional view taken along lineY-Y′ of FIG. 4A.

FIG. 5A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 5B is a cross-sectional view taken along lineX-X′ of FIG. 5A, and FIG. 5C is a cross-sectional view taken along lineY-Y′ of FIG. 5A.

FIG. 6A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 6B is a cross-sectional view taken along lineX-X′ of FIG. 6A, and FIG. 6C is a cross-sectional view taken along lineY-Y′ of FIG. 6A.

FIG. 7A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 7B is a cross-sectional view taken along lineX-X′ of FIG. 7A, and FIG. 7C is a cross-sectional view taken along lineY-Y′ of FIG. 7A.

FIG. 8A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 8B is a cross-sectional view taken along lineX-X′ of FIG. 8A, and FIG. 8C is a cross-sectional view taken along lineY-Y′ of FIG. 8A.

FIG. 9A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 9B is a cross-sectional view taken along lineX-X′ of FIG. 9A, and FIG. 9C is a cross-sectional view taken along lineY-Y′ of FIG. 9A.

FIG. 10A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 10B is a cross-sectional view taken along lineX-X′ of FIG. 10A, and FIG. 10C is a cross-sectional view taken alongline Y-Y′ of FIG. 10A.

FIG. 11A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 11B is a cross-sectional view taken along lineX-X′ of FIG. 11A, and FIG. 11C is a cross-sectional view taken alongline Y-Y′ of FIG. 11A.

FIG. 12A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 12B is a cross-sectional view taken along lineX-X′ of FIG. 12A, and FIG. 12C is a cross-sectional view taken alongline Y-Y′ of FIG. 12A.

FIG. 13A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 13B is a cross-sectional view taken along lineX-X′ of FIG. 13A, and FIG. 13C is a cross-sectional view taken alongline Y-Y′ of FIG. 13A.

FIG. 14A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 14B is a cross-sectional view taken along lineX-X′ of FIG. 14A, and FIG. 14C is a cross-sectional view taken alongline Y-Y′ of FIG. 14A.

FIG. 15A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 15B is a cross-sectional view taken along lineX-X′ of FIG. 15A, and FIG. 15C is a cross-sectional view taken alongline Y-Y′ of FIG. 15A.

FIG. 16A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 16B is a cross-sectional view taken along lineX-X′ of FIG. 16A, and FIG. 16C is a cross-sectional view taken alongline Y-Y′ of FIG. 16A.

FIG. 17A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 17B is a cross-sectional view taken along lineX-X′ of FIG. 17A, and FIG. 17C is a cross-sectional view taken alongline Y-Y′ of FIG. 17A.

FIG. 18A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 18B is a cross-sectional view taken along lineX-X′ of FIG. 18A, and FIG. 18C is a cross-sectional view taken alongline Y-Y′ of FIG. 18A.

FIG. 19A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 19B is a cross-sectional view taken along lineX-X′ of FIG. 19A, and FIG. 19C is a cross-sectional view taken alongline Y-Y′ of FIG. 19A.

FIG. 20A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 20B is a cross-sectional view taken along lineX-X′ of FIG. 20A, and FIG. 20C is a cross-sectional view taken alongline Y-Y′ of FIG. 20A.

FIG. 21A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 21B is a cross-sectional view taken along lineX-X′ of FIG. 21A, and FIG. 21C is a cross-sectional view taken alongline Y-Y′ of FIG. 21A.

FIG. 22A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 22B is a cross-sectional view taken along lineX-X′ of FIG. 22A, and FIG. 22C is a cross-sectional view taken alongline Y-Y′ of FIG. 22A.

FIG. 23A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 23B is a cross-sectional view taken along lineX-X′ of FIG. 23A, and FIG. 23C is a cross-sectional view taken alongline Y-Y′ of FIG. 23A.

FIG. 24A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 24B is a cross-sectional view taken along lineX-X′ of FIG. 24A, and FIG. 24C is a cross-sectional view taken alongline Y-Y′ of FIG. 24A.

FIG. 25A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 25B is a cross-sectional view taken along lineX-X′ of FIG. 25A, and FIG. 25C is a cross-sectional view taken alongline Y-Y′ of FIG. 25A.

FIG. 26A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 26B is a cross-sectional view taken along lineX-X′ of FIG. 26A, and FIG. 26C is a cross-sectional view taken alongline Y-Y′ of FIG. 26A.

FIG. 27A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 27B is a cross-sectional view taken along lineX-X′ of FIG. 27A, and FIG. 27C is a cross-sectional view taken alongline Y-Y′ of FIG. 27A.

FIG. 28A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 28B is a cross-sectional view taken along lineX-X′ of FIG. 28A, and FIG. 28C is a cross-sectional view taken alongline Y-Y′ of FIG. 28A.

FIG. 29A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 29B is a cross-sectional view taken along lineX-X′ of FIG. 29A, and FIG. 29C is a cross-sectional view taken alongline Y-Y′ of FIG. 29A.

FIG. 30A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 30B is a cross-sectional view taken along lineX-X′ of FIG. 30A, and FIG. 30C is a cross-sectional view taken alongline Y-Y′ of FIG. 30A.

FIG. 31A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 31B is a cross-sectional view taken along lineX-X′ of FIG. 31A, and FIG. 31C is a cross-sectional view taken alongline Y-Y′ of FIG. 31A.

FIG. 32A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 32B is a cross-sectional view taken along lineX-X′ of FIG. 32A, and FIG. 32C is a cross-sectional view taken alongline Y-Y′ of FIG. 32A.

FIG. 33A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 33B is a cross-sectional view taken along lineX-X′ of FIG. 33A, and FIG. 33C is a cross-sectional view taken alongline Y-Y′ of FIG. 33A.

FIG. 34A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 34B is a cross-sectional view taken along lineX-X′ of FIG. 34A, and FIG. 34C is a cross-sectional view taken alongline Y-Y′ of FIG. 34A.

FIG. 35A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 35B is a cross-sectional view taken along lineX-X′ of FIG. 35A, and FIG. 35C is a cross-sectional view taken alongline Y-Y′ of FIG. 35A.

FIG. 36A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 36B is a cross-sectional view taken along lineX-X′ of FIG. 36A, and FIG. 36C is a cross-sectional view taken alongline Y-Y′ of FIG. 36A.

FIG. 37A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 37B is a cross-sectional view taken along lineX-X′ of FIG. 37A, and FIG. 37C is a cross-sectional view taken alongline Y-Y′ of FIG. 37A.

FIG. 38A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 38B is a cross-sectional view taken along lineX-X′ of FIG. 38A, and FIG. 38C is a cross-sectional view taken alongline Y-Y′ of FIG. 38A.

FIG. 39A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 39B is a cross-sectional view taken along lineX-X′ of FIG. 39A, and FIG. 39C is a cross-sectional view taken alongline Y-Y′ of FIG. 39A.

FIG. 40A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 40B is a cross-sectional view taken along lineX-X′ of FIG. 40A, and FIG. 40C is a cross-sectional view taken alongline Y-Y′ of FIG. 40A.

FIG. 41A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 41B is a cross-sectional view taken along lineX-X′ of FIG. 41A, and FIG. 41C is a cross-sectional view taken alongline Y-Y′ of FIG. 41A.

FIG. 42A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 42B is a cross-sectional view taken along lineX-X′ of FIG. 42A, and FIG. 42C is a cross-sectional view taken alongline Y-Y′ of FIG. 42A.

FIG. 43A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 43B is a cross-sectional view taken along lineX-X′ of FIG. 43A, and FIG. 43C is a cross-sectional view taken alongline Y-Y′ of FIG. 43A.

FIG. 44A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 44B is a cross-sectional view taken along lineX-X′ of FIG. 44A, and FIG. 44C is a cross-sectional view taken alongline Y-Y′ of FIG. 44A.

FIG. 45A is a plan view illustrating the method for manufacturing anonvolatile semiconductor memory according to the embodiment of thepresent invention, FIG. 45B is a cross-sectional view taken along lineX-X′ of FIG. 45A, and FIG. 45C is a cross-sectional view taken alongline Y-Y′ of FIG. 45A.

FIG. 46 is a cross-sectional view of an SGT flash memory of the relatedart.

DETAILED DESCRIPTION

An embodiment of the present invention will be described hereinafterwith reference to the drawings. The present invention is not limited tothe following embodiment.

FIG. 1 illustrates a cross-sectional view of a nonvolatile semiconductormemory transistor according to an embodiment of the present invention.

As illustrated in FIG. 1, the nonvolatile semiconductor memorytransistor is configured such that a source region 303, a channel region304, and a drain region 302 are formed in this order from the substrateside and constitute a cylindrical island-shaped semiconductor 301. Thenonvolatile semiconductor memory transistor further includes a floatinggate 306 arranged so as to surround the outer periphery of the channelregion 304 with a tunnel insulating film 305 interposed between thefloating gate 306 and the channel region 304, a control gate 308 aarranged so as to surround the outer periphery of the floating gate 306with an inter-polysilicon insulating film 307 interposed between thecontrol gate 308 a and the floating gate 306, and a control gate line308 electrically connected to the control gate 308 a and extending in apredetermined direction (to the right in FIG. 1).

The inter-polysilicon insulating film 307 is arranged so as to beinterposed between the floating gate 306 and the lower and inner sidesurfaces of the control gate 308 a and between the floating gate 306 andthe lower surface of the control gate line 308.

As illustrated in FIG. 1, the floating gate 306 includes a firstfloating gate portion 306 b facing the lower surface of the control gate308 a, and a second floating gate portion 306 c facing the lower surfaceof the control gate line 308. The first floating gate portion 306 b andthe second floating gate portion 306 c enable an increase in capacitance(electrostatic capacitance) consisting of first capacitance between thefloating gate 306 and the control gate 308 a and second capacitancebetween the floating gate 306 and the control gate line 308.

FIG. 2A, FIG. 2B, and FIG. 2C illustrate a plan view of a nonvolatilesemiconductor memory according to this embodiment, an X-X′cross-sectional view of FIG. 2A, and a Y-Y′ cross-sectional view of FIG.2A, respectively.

As illustrated in FIG. 2A and FIG. 2B, the nonvolatile semiconductormemory is configured such that a plurality of (in the figures, three)nonvolatile semiconductor memory transistors 201, 202, and 203 eachhaving the structure illustrated in FIG. 1 are arranged in a pluralityof row directions among row and column directions on a silicon substrate101 so as to be aligned in a straight line at substantially equal anglesand intervals.

In the nonvolatile semiconductor memory illustrated in FIG. 2A to FIG.2C, the nonvolatile semiconductor memory transistor 201 is arranged inthe first column in the column direction among the row and columndirections on the silicon substrate 101.

As illustrated in FIG. 2A, FIG. 2B, and FIG. 2C, in the nonvolatilesemiconductor memory transistor 201, a source region 121, a channelregion 124, and a drain region 156 are formed in this order from thesilicon substrate 101 side, and constitute an island-shapedsemiconductor 113.

The nonvolatile semiconductor memory transistor 201 includes a floatinggate 139 that is arranged so as to surround the outer periphery of thechannel region 124 in such a manner that a tunnel insulating film 132 isinterposed between the floating gate 139 and the channel region 124, anda control gate 153 a that is arranged so as to surround the outerperiphery of the floating gate 139 in such a manner that aninter-polysilicon insulating film 142 is interposed between the controlgate 153 a and the floating gate 139. A control gate line 153 extendingin a predetermined direction (to the left and right in FIG. 2B) betweenthe nonvolatile semiconductor memory transistors 201 and 202 iselectrically connected to the control gate 153 a (in FIG. 2B, thecontrol gate 153 a and the control gate line 153 are illustrated in anintegrated manner).

As illustrated in FIG. 2B, the floating gate 139 includes a portionfacing the lower surface of the control gate 153 a (which corresponds tothe first floating gate portion 306 b in FIG. 1), and a portion facingthe lower surface of the control gate line 153 (which corresponds to thesecond floating gate portion 306 c in FIG. 1).

In the nonvolatile semiconductor memory transistor 201, an oxide film(first insulating film) 128 that is thicker than the tunnel insulatingfilm 132 and the inter-polysilicon insulating film 142 is arranged onthe lower surface of the floating gate 139. Here, the thickness of theoxide film 128 is larger than the thickness of the tunnel insulatingfilm 132 and the inter-polysilicon insulating film 142. However, this isnot meant to be limiting, and the oxide film 128 may be thicker than atleast one of the tunnel insulating film 132 and the inter-polysiliconinsulating film 142.

In the nonvolatile semiconductor memory illustrated in FIG. 2A to FIG.2C, the nonvolatile semiconductor memory transistor 202 is arranged inthe second column in the column direction among the row and columndirections on the silicon substrate 101.

As illustrated in FIG. 2A, FIG. 2B, and FIG. 2C, in the nonvolatilesemiconductor memory transistor 202, a source region 122, a channelregion 125, and a drain region 157 are formed in this order from thesilicon substrate 101 side, and constitute an island-shapedsemiconductor 114.

The nonvolatile semiconductor memory transistor 202 includes a floatinggate 140 that is arranged so as to surround the outer periphery of thechannel region 125 in such a manner that a tunnel insulating film 133 isinterposed between the floating gate 140 and the channel region 125, anda control gate 153 b that is arranged so as to surround the outerperiphery of the floating gate 140 in such a manner that theinter-polysilicon insulating film 142 is interposed between the controlgate 153 b and the floating gate 140. The control gate line 153extending in a predetermined direction (to the left and right in FIG.2B) between the nonvolatile semiconductor memory transistors 202 and 203is electrically connected to the control gate 153 b (in FIG. 2B, thecontrol gate 153 b and the control gate line 153 are illustrated in anintegrated manner).

As illustrated in FIG. 2B, the floating gate 140 includes a portionfacing the lower surface of the control gate 153 b (which corresponds tothe first floating gate portion 306 b in FIG. 1), and a portion facingthe lower surface of the control gate line 153 (which corresponds to thesecond floating gate portion 306 c in FIG. 1).

In the nonvolatile semiconductor memory transistor 202, the oxide film(first insulating film) 128 that is thicker than the tunnel insulatingfilm 133 and the inter-polysilicon insulating film 142 is arranged onthe lower surface of the floating gate 140. Here, the thickness of theoxide film 128 is larger than the thickness of the tunnel insulatingfilm 133 and the inter-polysilicon insulating film 142. However, this isnot meant to be limiting, and the oxide film 128 may be thicker than atleast one of the tunnel insulating film 133 and the inter-polysiliconinsulating film 142.

In the nonvolatile semiconductor memory illustrated in FIG. 2A to FIG.2C, the nonvolatile semiconductor memory transistor 203 is arranged inthe third column in the column direction among the row and columndirections on the silicon substrate 101.

As illustrated in FIG. 2A, FIG. 2B, and FIG. 2C, in the nonvolatilesemiconductor memory transistor 203, a source region 123, a channelregion 126, and a drain region 158 are formed in this order from thesilicon substrate 101 side, and constitute an island-shapedsemiconductor 115.

The nonvolatile semiconductor memory transistor 203 includes a floatinggate 141 that is arranged so as to surround the outer periphery of thechannel region 126 in such a manner that a tunnel insulating film 134 isinterposed between the floating gate 141 and the channel region 126, anda control gate 153 c that is arranged so as to surround the outerperiphery of the floating gate 141 in such a manner that theinter-polysilicon insulating film 142 is interposed between the controlgate 153 c and the floating gate 141. The control gate line 153extending in a predetermined direction (to the left and right in FIG.2B) is electrically connected to the control gate 153 c (in FIG. 2B, thecontrol gate 153 c and the control gate line 153 are illustrated in anintegrated manner).

As illustrated in FIG. 2B, the floating gate 141 includes a portionfacing the lower surface of the control gate 153 c (which corresponds tothe first floating gate portion 306 b in FIG. 1), and a portion facingthe lower surface of the control gate line 153 (which corresponds to thesecond floating gate portion 306 c in FIG. 1).

In the nonvolatile semiconductor memory transistor 203, the oxide film(first insulating film) 128 that is thicker than the tunnel insulatingfilm 134 and the inter-polysilicon insulating film 142 is arranged onthe lower surface of the floating gate 141. Here, the thickness of theoxide film 128 is larger than the thickness of the tunnel insulatingfilm 134 and the inter-polysilicon insulating film 142. However, this isnot meant to be limiting, and the oxide film 128 may be thicker than atleast one of the tunnel insulating film 134 and the inter-polysiliconinsulating film 142.

In the nonvolatile semiconductor memory illustrated in FIG. 2A to FIG.2C, the source regions 121, 122, and 123 of the nonvolatilesemiconductor memory transistors 201, 202, and 203 are formed in lowerportions of the island-shaped semiconductors 113, 114, and 115 of thenonvolatile semiconductor memory transistors 201, 202, and 203,respectively, and are electrically connected to a source line 120 on thetop of the silicon substrate 101. Further, the drain regions 156, 157,and 158 of the nonvolatile semiconductor memory transistors 201, 202,and 203 are connected to bit lines 183, 184, and 185 via contacts 176,177, and 178, respectively.

As illustrated in FIG. 2A to FIG. 2C, the control gate line 153 extendsin a predetermined direction so as to connect the control gates 153 a,153 b, and 153 c of the adjacent island-shaped semiconductors 113, 114,and 115.

An example of a manufacturing process for forming a memory cell arraystructure of the nonvolatile semiconductor memory according to theembodiment of the present invention will be described hereinafter withreference to FIGS. 3A to 45C.

Referring to FIG. 3A to FIG. 3C, an oxide film 102 is formed on the topof a silicon substrate 101. After that, a nitride film 103 is depositedfrom above the oxide film 102.

Subsequently, referring to FIG. 4A to FIG. 4C, resists 104, 105, and 106for forming island-shaped semiconductors 113, 114, and 115 (see FIG. 2Ato FIG. 2C) are formed at predetermined positions on the top of thenitride film 103.

Subsequently, referring to FIG. 5A to FIG. 5C, the nitride film 103 andthe oxide film 102 are etched by reactive ion etching (RIE) using theresists 104, 105, and 106 as masks. Thereby, a hard mask made of anitride film 107 and an oxide film 110, a hard mask made of a nitridefilm 108 and an oxide film 111, and a hard mask made of a nitride film109 and an oxide film 112 are formed on the top of the silicon substrate101.

Subsequently, referring to FIG. 6A to FIG. 6C, further, the siliconsubstrate 101 is etched by reactive ion etching using the resists 104,105, and 106 as masks, and the island-shaped semiconductors 113, 114,and 115 are formed.

Subsequently, referring to FIG. 7A to FIG. 7C, the resists 104, 105, and106 are stripped.

Subsequently, referring to FIG. 8A to FIG. 8C, an oxide film 116 isdeposited on the outer peripheral wall surfaces of the island-shapedsemiconductors 113, 114, and 115 and the bottom surfaces of the gapsbetween the island-shaped semiconductors 113, 114, and 115.

Subsequently, referring to FIG. 9A to FIG. 9C, the oxide film 116 isetched, and oxide film sidewalls 117, 118, and 119 are formed on theouter peripheral wall surfaces of the island-shaped semiconductors 113,114, and 115, respectively.

Subsequently, referring to FIG. 10A to FIG. 10C, arsenic (see arrows As)is injected into the silicon substrate 101 to form a source line 120that is an n-type (second conductivity type) semiconductor on thesurface of the silicon substrate 101. Further, source regions 121, 122,and 123 are formed in lower portions of the island-shaped semiconductors113, 114, and 115 (see FIG. 9A to FIG. 9C), respectively, so as to beelectrically connected to the source line 120. At this time, channelregions 124, 125, and 126 are formed between the source region 121 andthe nitride film 107 and oxide film 110, between the source region 122and the nitride film 108 and oxide film 111, and between the sourceregion 123 and the nitride film 109 and oxide film 112, respectively.

Subsequently, referring to FIG. 11A to FIG. 11C, the oxide filmsidewalls 117, 118, and 119 are removed by etching.

Subsequently, referring to FIG. 12A to FIG. 12C, an oxide film 127 isdeposited on the top of the source line 120, on the top of the nitridefilms 107, 108, and 109, and on the outer peripheral wall surfaces ofthe island-shaped semiconductors 113, 114, and 115 (see FIG. 9A to FIG.9C) so that the oxide film 127 on the top of the source line 120 and thenitride films 107, 108, and 109 becomes thick while the oxide film 127on the outer peripheral wall surfaces becomes thin.

Subsequently, referring to FIG. 13A to FIG. 13C, the portions of theoxide film 127 deposited on the outer peripheral wall surfaces of theisland-shaped semiconductors 113, 114, and 115 (see FIG. 9A to FIG. 9C)are etched by isotropic etching. Therefore, even after the removal ofthe portions of the oxide film 127 on the outer peripheral wall surfacesof the island-shaped semiconductors 113, 114, and 115 by etching, anoxide film 128 which is an insulating film remains on the gaps betweenthe adjacent island-shaped semiconductors 113, 114, and 115 (see FIG. 9Ato FIG. 9C) and on the top of the source line 120. Further, oxide films129, 130, and 131 remain in a disk shape on the top of the nitride films107, 108, and 109, respectively. In this manner, the oxide film 127remains as the oxide films 129, 130, and 131 because of the followingreason: Referring to FIG. 12A to FIG. 12C, the oxide film 127 isdeposited on the top of the source line 120 and on the top of thenitride films 107, 108, and 109 so as to become thick while the oxidefilm 127 is deposited on the outer peripheral wall surfaces of theisland-shaped semiconductors 113, 114, and 115 so as to become thin,and, additionally, the oxide film 127 has been subjected to isotropicetching in which etching progresses at the same speed in all directions.The oxide film 128 remaining on the top of the source line 120 becomesthe first insulating film 128 (see FIG. 2B to FIG. 2C) in resultingnonvolatile semiconductor memory transistors 201, 202, and 203,respectively, and contributes to the reduction in the capacitancebetween the floating gates 139, 140, and 141 and the source line 120.

Subsequently, referring to FIG. 14A to FIG. 14C, tunnel insulating films132, 133, and 134 are formed on the outer peripheral wall surfaces ofthe island-shaped semiconductors 113, 114, and 115 (see FIG. 9A to FIG.9C), respectively, by gate oxidation.

Subsequently, referring to FIG. 15A to FIG. 15C, a polysilicon layer 135that becomes a floating gate is deposited using a conductive materialsuch as polysilicon.

Subsequently, referring to FIG. 16A to FIG. 16C, resists 136, 137, and138 are formed so as to cover the island-shaped semiconductors 113, 114,and 115 that are adjacent to each other (see FIG. 9A to FIG. 9C),respectively. The resists 136, 137, and 138 have grooves that arearranged between the resists 136 and 137 and between the resists 137 and138 and that extend in a direction perpendicular to the predetermineddirection (to the left and right in FIG. 16B) in which the control gateline 153 extends. The control gate line 153 extends in the predetermineddirection (see FIG. 2A to FIG. 2C) so as to connect the control gates153 a, 153 b, and 153 c of the adjacent island-shaped semiconductors113, 114, and 115 (see FIG. 9A to FIG. 9C).

Subsequently, referring to FIG. 17A to FIG. 17C, the polysilicon layer135 is separated from portions that are on the oxide film 128 and thatare lower regions of the grooves by etching using the resists 136, 137,and 138 as masks, and floating gates 139, 140, and 141 are formed forthe island-shaped semiconductors 113, 114, and 115, respectively (seeFIG. 9A to FIG. 9C).

Subsequently, referring to FIG. 18A to FIG. 18C, the resists 136, 137,and 138 are stripped.

Subsequently, referring to FIG. 19A to FIG. 19C, an inter-polysiliconinsulating film 142 is formed from above the oxide film 128 on the topof the source line 120, the floating gates 139, 140, and 141, and theoxide films 129, 130, and 131. After that, a polysilicon layer 143 isdeposited on the top of the inter-polysilicon insulating film 142, andplanarized using CMP (Chemical Mechanical Polishing) so that the tipportions of the oxide films 129, 130, and 131 are exposed. Here, theinter-polysilicon insulating film 142 may be formed of either a layeredstructure of an oxide film, an oxide film, a nitride film, and an oxidefilm, or of a high dielectric film.

Subsequently, referring to FIG. 20A to FIG. 20C, the oxide films 129,130, and 131 are removed by etching.

Subsequently, referring to FIG. 21A to FIG. 21C, the polysilicon layer143 is etched back to a predetermined depth by etching.

Subsequently, referring to FIG. 22A to FIG. 22C, the exposed portions ofthe inter-polysilicon insulating film 142 are removed by etching.

Subsequently, referring to FIG. 23A to FIG. 23C, the exposed portions ofthe floating gates 139, 140, and 141 and a portion of the polysiliconlayer 143 are removed by etching. With this etching, the gate length ofthe resulting nonvolatile semiconductor memory transistors 201, 202, and203 is determined.

Subsequently, referring to FIG. 24A to FIG. 24C, an oxide film 144 isdeposited. After that, a nitride film 145 is deposited from above theoxide film 144.

Subsequently, referring to FIG. 25A to FIG. 25C, the nitride film 145and the oxide film 144 are etched by anisotropic etching. Further, thenitride film 145 and the oxide film 144 (see FIG. 24A to FIG. 24C)remain in a sidewall shape on the outer peripheral wall surfaces of theisland-shaped semiconductors 113, 114, and 115 and the tunnel insulatingfilms 132, 133, and 134, and on the outer peripheral wall surfaces ofthe nitride film 107 and oxide film 110, the nitride film 108 and oxidefilm 111, and the nitride film 109 and oxide film 112. Therefore, aninsulating film sidewall 501 made of a nitride film 146 and an oxidefilm 149, an insulating film sidewall 502 made of a nitride film 147 andan oxide film 150, and an insulating film sidewall 503 made of a nitridefilm 148 and an oxide film 151 are formed for the island-shapedsemiconductors 113, 114, and 115, respectively (see FIG. 9A to FIG. 9C).

Subsequently, referring to FIG. 26A to FIG. 26C, a resist 152 forforming a control gate line 153 so as to extend to the left and right inFIG. 26A and FIG. 26B to cover the insulating film sidewalls 501, 502,503 and the nitride films 107, 108, and 109 is formed.

Subsequently, referring to FIG. 27A to FIG. 27C, the polysilicon layer143, the inter-polysilicon insulating film 142, and the floating gates139, 140, and 141 are etched using the insulating film sidewalls 501,502, and 503 and the resist 152 as masks to form control gates 153 a,153 b, and 153 c and the control gate line 153. Thus, in the resultingnonvolatile semiconductor memory transistors 201, 202, and 203, astructure in which the floating gates 139, 140, and 141 include portionsfacing the lower surfaces of the control gates 153 a, 153 b, and 153 c,respectively, and also include portions facing the lower surfaces of thecontrol gate line 153 is formed.

Subsequently, referring to FIG. 28A to FIG. 28C, the exposed portions ofthe oxide film 128 are etched, and a first insulating film 128 isformed.

Subsequently, referring to FIG. 29A to FIG. 29C, the resist 152 isstripped, and the surface layer portions of the control gate line 153,the floating gates 139, 140, and 141, and the source line 120 areoxidized to deposit an oxide film 154 on the top of the control gateline 153 and the floating gates 139, 140, and 141 and to deposit anoxide film 155 on the top of the source line 120.

Subsequently, referring to FIG. 30A to FIG. 30C, the nitride films 107,108, and 109 and the nitride films 146, 147, and 148 are stripped.

Subsequently, referring to FIG. 31A to FIG. 31C, the oxide films 110,111, and 112, the oxide films 149, 150, and 151, the oxide films 154 and155, and the tunnel insulating films 132, 133, and 134 are stripped, andthe channel regions 124, 125, and 126 of the island-shapedsemiconductors 113, 114, and 115 (see FIG. 9A to FIG. 9C) are exposed.

Subsequently, referring to FIG. 32A to FIG. 32C, arsenic (see arrows As)is injected into the top layer portions of the channel regions 124, 125,and 126 of the island-shaped semiconductors 113, 114, and 115,respectively, and drain regions 156, 157, and 158 that are n-typesemiconductors are formed.

Subsequently, referring to FIG. 33A to FIG. 33C, a nitride film 159 isdeposited so as to cover the island-shaped semiconductors 113, 114, and115 (see FIG. 9A to FIG. 9C) and the source line 120.

Subsequently, referring to FIG. 34A to FIG. 34C, the nitride film 159 isetched so as to remain in a sidewall shape on the side walls of theisland-shaped semiconductors 113, 114, and 115 (see FIG. 9A to FIG. 9C)and on the side wall of the control gate line 153 to form nitride filmsidewalls 160, 161, 162, and 163, respectively.

Subsequently, referring to FIG. 35A to FIG. 35C, in order to reduce theresistance, the island-shaped semiconductors 113, 114, and 115, thecontrol gate line 153, and the source line 120 are subjected to asilicide process using a metal material, and metal semiconductorcompounds 164, 165, 166, 167, 168, and 169 are formed.

Subsequently, referring to FIG. 36A to FIG. 36C, a contact stopper 170is deposited using an insulating material so as to cover theisland-shaped semiconductors 113, 114, and 115 and the nitride filmsidewalls 160, 161, 162, and 163. Additionally, an interlayer film 171is deposited on the top layer of the contact stopper 170, and thereafterplanarized using CMP.

Subsequently, referring to FIG. 37A to FIG. 37C, a resist 172 forforming contact holes 173, 174, and 175 (see FIG. 38A to FIG. 38C) isformed at a predetermined position on the top of the interlayer film171.

Subsequently, referring to FIG. 38A to FIG. 38C, the interlayer film 171is etched using the resist 172 as a mask to form the contact holes 173,174, and 175, and the surface portions of the contact stopper 170 areexposed.

Subsequently, referring to FIG. 39A to FIG. 39C, the resist 172 isstripped.

Subsequently, referring to FIG. 40A to FIG. 40C, the portions of thecontact stopper 170 which are located on the bottom portions of thecontact holes 173, 174, and 175 are removed by etching.

Subsequently, referring to FIG. 41A to FIG. 41C, contacts 176, 177, and178 are formed using a conductive material in the contact holes 173,174, and 175, respectively, and are electrically connected to the drainregions 156, 157, and 158 of the island-shaped semiconductors 113, 114,and 115 (see FIG. 9A to FIG. 9C), respectively.

Subsequently, referring to FIG. 42A to FIG. 42C, a metal 179 isdeposited using a metal material on the top of the interlayer film 171and the contacts 176, 177, and 178.

Subsequently, referring to FIG. 43A to FIG. 43C, resists 180, 181, and182 for forming bit lines 183, 184, and 185 of the resulting nonvolatilesemiconductor memory transistors 201, 202, and 203, respectively, areformed on the top of the metal 179.

Subsequently, referring to FIG. 44A to FIG. 44C, the metal 179 is etchedusing the resists 180, 182, and 183 as masks to form the bit lines 183,184, and 185.

Subsequently, referring to FIG. 45A to FIG. 45C, the resists 180, 181,and 182 are stripped. Therefore, the formation of the nonvolatilesemiconductor memory illustrated in FIG. 2A to FIG. 2C is completed.

It is to be understood that the present invention can embrace variousembodiments and modifications without departing from the broad spiritand scope of the present invention. In addition, the foregoingembodiment is used to describe an example of the present invention, andis not intended to limit the scope of the present invention.

The invention claimed is:
 1. A nonvolatile semiconductor memory transistor comprising: an island-shaped semiconductor having a channel region; a floating gate surrounding an outer periphery of the channel region and a tunnel insulating film interposed between the floating gate and the channel region; a control gate surrounding an outer periphery of the floating gate and an inter-polysilicon insulating film interposed between the control gate and the floating gate; and a control gate line electrically connected to the control gate and extending in a predetermined direction, wherein the inter-polysilicon insulating film is interposed between the floating gate and a lower surface and an inner side surface of the control gate and between the floating gate and a lower surface of the control gate line. 